1. Field of the Invention
The present invention relates to a method of adjusting group-delay characteristics of piezoelectric resonators and more particularly, the present invention relates to a method of adjusting group-delay characteristics of piezoelectric resonators included in a ladder type filter.
2. Description of the Related Art
A conventional device shown in FIG. 9 includes a synthetic resin material 2, such as silicon oil or silicon rubber that is not cured and that has been adhered onto, for example, an upper surface or a lower surface of a piezoelectric resonator 1. Subsequently, the synthetic resin material 2 has been cured so as to be used for adjustment of group-delay characteristics of a piezoelectric resonator 1. The soft material is adhered onto the piezoelectric resonator 1 to perform damping of Qm characteristics, thereby allowing the group-delay characteristics to be adjusted.
In adhering the uncured materials onto the piezoelectric resonator, however, quantitative control for the adhesion materials is difficult. This causes variation in the amount of the adhesion materials by approximately 10%. Also, the difficulty in the quantitative control of the uncured material makes it difficult to selectively perform the adjustment corresponding to the initial group-delay characteristics of the individual piezoelectric resonators. To solve these problems, for example, preliminary examinations and periodical quantitative checking of the uncured materials must be performed. In addition, in using the uncured material, since determination of adhesion portions for the piezoelectric resonator is difficult, as shown in FIG. 9, the uncured material occasionally flows to a peripheral surface of the piezoelectric resonator. When synthetic resin material is applied on predetermined portions of the piezoelectric resonators, there are cases where characteristics of devices using the piezoelectric resonators, such as the piezoelectric filter, are reduced depending on the adhesion portion of the uncured material. In addition, use of the uncured material requires heat-curing after the adhesion thereof, thereby making the adjustment to be difficult. In this case, heating may cause reduction in the characteristics of the piezoelectric resonators.
In order to solve the problems described above, preferred embodiments of the present invention provide a method of adjusting group-delay characteristics of piezoelectric resonators that is performed easily and without affecting electrical characteristics thereof.
According to one preferred embodiment of the present invention, a method of adjusting group-delay characteristics of piezoelectric resonators includes preparing members having multiple sizes and each having a maximum Young""s modulus of about 100 Mpa, measuring initial group-delay characteristics of the piezoelectric resonators, selecting the members having a size which is suitable for use with the piezoelectric resonators for adjusting the initial group-delay characteristics measured in the measuring step to achieve a required group-delay characteristics, and adhering the members selected in the selecting step onto the piezoelectric resonators.
According to another preferred embodiment of the present invention, a method of adjusting group-delay characteristics of piezoelectric resonators includes measuring as a preliminary examination for measuring group-delay characteristics of the piezoelectric resonators, preparing members having various sizes and a maximum Young""s modulus of about 100 MPa and each being formed to be adapted for adjustment thereof to achieve required group-delay characteristics of the piezoelectric resonators that will be manufactured in a later step, and adhering the members onto the piezoelectric resonators.
In one of the above-described methods of adjusting group-delay characteristics of piezoelectric resonators, each of the members may be a silicon sheet having an adherent portion on one surface thereof.
Also, in one of the above-described methods of adjusting group-delay characteristics of piezoelectric resonators, each of the members may be a cured synthetic resin material.
As described above, by adhering the members having the maximum Young""s modulus of about 100 MPa onto the individual piezoelectric resonators, damping of Qm characteristics of the individual piezoelectric resonators is performed, and the group-delay characteristics are easily and accurately adjusted. In this case, using cured members allows control of the amount of materials adhered onto the piezoelectric resonators. Also, the members determined to be adhered are selected based on the initial group-delay characteristics of the individual piezoelectric resonators, and the selected members are then adhered. According to this arrangement, the group-delay characteristics can be adjusted selectively corresponding to the individual piezoelectric resonators.
Alternatively, preliminary examinations are carried out to measure the initial group-delay characteristics, members of a size determined to be suitable for adhesion onto the group-delay characteristics of the piezoelectric resonators that will be manufactured in a later step are prepared, and the members are adhered onto the individual piezoelectric resonators. This also allows the group-delay characteristics to be adjusted.
In the above-described methods, since the members are already cured, portions of adhesion of the members which are joined onto the piezoelectric resonators are accurately specified. Also, the materials of the members do not flow to undesired locations, reduction in the characteristics can be prevented. In addition, the described materials used for forming the members require no heat treatments after they are adhered.
When the silicon sheets each having an adherent portion on one surface are used to form the members for the methods described above, they can be precut to have a predetermined size. This facilitates adhesion of the silicon sheets onto the piezoelectric resonators.
Also, instead of the members having a sheet-like configuration, synthetic resin materials which are formed to have a predetermined size may be used as the members so as to produce equivalent advantages.
In this way, according to various preferred embodiments of the present invention, the group-delay characteristics of the piezoelectric resonators can be implemented easily. For example, a method according to preferred embodiments of the present invention does not require processing such as heat treatment. Also, preferred embodiments of the present invention allow precise adjustment to be achieved, thereby minimizing variation in the amount of the sheet members adhered onto the individual piezoelectric resonators. In addition, preferred embodiments of the present invention allow the sheet members to be adhered onto required portions of the individual piezoelectric resonators, thereby preventing reduction in the characteristics thereof, which can be caused depending on the portions where the members are adhered. Furthermore, preferred embodiments of the present invention do not require heat treatment for curing the sheet members, thereby preventing the reduction in the characteristics, which can be caused by heating.
The described and other objects, features and advantages of the present invention will be more readily apparent from a detailed description given below with reference to the accompanying drawings.